1. Field of the Invention
The present invention relates to a communication apparatus used in a communication system in which transmission and reception is performed through a transmission medium such as a human body.
2. Description of the Related Art
Due to recent developments in technology, communication methods in which electric fields are induced in the human body or the like (so-called electric field communication) have been proposed as totally new communication methods. An example of such a communication system is disclosed, for example, in PCT Japanese Translation Patent Publication No. 11-509380. In the communication system, a transmitter supplies an electric field corresponding to a modulation signal obtained by modulating an information signal to a human body serving as a transmission medium, and a receiver detects the electric field transmitted through the human body and performs demodulation to obtain the original signal corresponding to the electric field.
In the electric field communication mentioned above, a signal is transmitted by capacitive coupling, instead of causing a through-current to flow to a transmission medium. Thus, it is desirable that the capacitive coupling between a transmission electrode and the transmission medium, the transmission electrode providing a capacitive coupling between the transmission medium and a transmission circuit of a transmitter, and the capacitive coupling between a reception electrode and the transmission medium, the reception electrode providing a capacitive coupling between the transmission medium and a reception circuit of a receiver, be large.
However, in the case that the transmitter or receiver described above is provided in the casing of an electronic apparatus such as a cellular phone, a space is formed between the internal surface of the casing and the transmission electrode of the transmitter or between the internal surface of the casing and the reception electrode of the receiver. Hence, the capacitive coupling between the transmission or reception electrode and a transmission medium is reduced, and a transmission signal thus becomes faint. Furthermore, due to a variation in the space between the internal surface of the casing and the transmission or reception electrode, the signal intensity varies.